Periodontal disease and subsequent risk of cardiovascular outcome and all-cause mortality: A meta-analysis of prospective studies

Studies reported periodontal disease (PD) periodontal disease is associated with many systemic diseases, including cardiovascular outcomes and all-cause mortality. However, the precise mechanistic link for these relationship remained unclear. We therefore performed a meta-analysis of cohort studies to investigate the association of PD with the risk of cardiovascular outcomes and all-cause mortality. We systematically searched the databases of PubMed, EmBase, and the Cochrane library to identify eligible studies until April 2023. The investigated outcomes included major adverse cardiovascular events (MACEs), coronary heart disease (CHD), myocardial infarction (MI), stroke, cardiac death, and all-cause mortality. The summary relative risk (RR) with 95% confidence interval (CI) were calculated using the random-effects model. Thirty-nine cohort studies with 4,389,263 individuals were selected for final meta-analysis. We noted PD were associated with elevated risk of MACEs (RR: 1.24; 95%CI: 1.15–1.34; P<0.001), CHD (RR: 1.20; 95%CI: 1.12–1.29; P<0.001), MI (RR: 1.14; 95%CI: 1.06–1.22; P = 0.001), stroke (RR: 1.26; 95%CI: 1.15–1.37; P<0.001), cardiac death (RR: 1.42; 95%CI: 1.10–1.84; P = 0.007), and all-cause mortality (RR: 1.31; 95%CI: 1.07–1.61; P = 0.010). Sensitivity analyses indicated the pooled conclusions for cardiovascular outcomes and all-cause mortality are robustness. The associations of PD with the risk of ardiovascular outcomes and all-cause mortality could affected by region, study design, PD definition, follow-up duration, and study quality. This study found the risk of cardiovascular outcomes and all-cause mortality were elevated in PD patients, and the intervention for PD should be applied to prevent the risk of cardiovascular outcomes.


Introduction
Cardiovascular disease (CVD) accounted for 17.8 million deaths worldwide in 2017, and these CVD deaths were caused by ischemic heart disease and stroke were 50% and 35%, respectively [1].Moreover, ischemic heart disease and stroke were the top-ranked causes for disabilityadjusted life-years in patients aged 50 years or older [2].Managing patients at risk of CVD are important for prevent hospital admissions, and improve the quality of life.Currently, the independent risk factors for CVD included age, smoking, obesity, hypertension, diabetes mellitus, reduced high-density lipoprotein (HDL), and elevated low density lipoprotein (LDL) [3][4][5].An additional risk factor should be identified for primary and secondary prevention and improve the prognosis of CVD.
Periodontal disease (PD) is a chronic inflammatory disease, which caused by dental plaque through attacks the immune defense line of periodontal tissue.The clinical manifestations of PD included gingiva bleeding, periodontal pocket, alveolar bone resorption, and tooth loss.PD is highly prevalent accounting for 20-50% of the global population, which could cause a loss of clinical attachment, and the progressive of PD could induce the loosening of teeth or even to the loss of teeth [6].Study have demonstrated PD it not only a common chronic infectious and inflammatory oral disease, but also associated with the risk of several systemic disease, including rheumatoid arthritis, diabetes mellitus, chronic obstructive pulmonary disease, depression, and Alzheimer's disease [7][8][9][10][11].Nowadays, more and more attention has been paid to the association of PD with the risk of cardiovascular outcome and all-cause mortality.Several systematic review and meta-analyses were performed to assess the association between PD with the risk of cardiovascular outcomes [12][13][14][15], whereas the exploratory analyses for these relationship remained unclear.Therefore, we conducted this systematic review and meta-analysis to evaluate the association of PD with the risk of cardiovascular outcome and all-cause mortality.

Literature search and selection criteria
The Meta-analysis Of Observational Studies in Epidemiology protocol was applied to perform and report this systematic review and meta-analysis [16].Cohort study assess the association of PD with the risk of cardiovascular outcome and all-cause mortality was potential eligible in this study, and the publication language and status were not restricted.The databases of PubMed, EmBase, and the Cochrane library were systematically searched for eligible studies from their inception until April 2023, and using the following search terms: ("Periodontal disease" OR "tooth loss" OR "missing teeth" OR "periodontal") AND ("cardiovascular disease" OR "atrial fibrillation" OR "heart failure" OR "stroke" OR "cerebrovascular" OR "angina" OR "acute coronary syndrome").We also manually reviewed the reference lists of relevant original article and review to identify any new study met the inclusion criteria.
The literature search and study selection were independently performed by 2 reviewers following the standardized flow, and conflicts between reviewers was resolved by discussed with a third reviewer until a consensus was reached.The details of inclusion criteria included: (1) Participants: adult population free of CVD at initially; (2) exposure: moderate or severe PD; (3) Control: individuals without PD or mild PD; (4) Outcomes: the study should reported at least 1 of major adverse cardiovascular events (MACE), coronary heart disease (CHD), myocardial infarction (MI), stroke, cardiac death, and all-cause mortality; and (5) Study design: cohort study, irrespective prospective or retrospective cohort design.There was no restriction was placed on the minimum number of participants.The study was excluded if they met: (1) cross-sectional or case-control design; (2) the effect estimate was presented without 95% confidence intervals (CIs); or (3) study did not reported cardiovascular outcome or all-cause mortality.

Data extraction and quality assessment
Two reviewers independently performed data collection, and inconsistent results between reviewers was settled by a third reviewer referring to full-text of article.The abstracted information in each included study included first authors' surname, publication year, region, study design, sample size, range of individuals' age, male proportion, the definition of PD, reported outcomes, follow-up duration, and adjusted factors.The Newcastle-Ottawa Scale (NOS) was used to assess the methodological quality of observational studies in meta-analysis, which including selection (4 items), comparability (1 item), and outcome (3 items) domains, and the "star system" in individual study ranged from 0-9.Study with 7-9 stars was regarded as high quality, 4-6 stars was defined as moderate quality, and with 0-3 stars was considered as low quality [17].The quality assessment was independently performed by 2 reviewers, and an additional reviewer was examined and adjudicated disagreement between reviewers through referring to the original article.

Statistical analysis
The association of PD with the risk of cardiovascular outcomes and all-cause mortality based on the effect estimate with 95%CI in individual study.The summary relative risk (RR) and 95%CI were calculated using the random-effects model with Mantel-Haenszel Statistics, which considering the underlying varies across included studies [18,19].The I 2 and Cochren Q statistic was applied to assess the heterogeneity across included studies, and I 2 � 50.0% or P < 0.10 was defined as significant heterogeneity [20,21].Sensitivity analysis was applied to assess the robustness of pooled conclusion through sequential removing single study [22].Subgroup analyses were conducted based on region, study design, gender, PD definition, follow-up duration, adjusted level, and study quality, and the differences between subgroups were assessed using interaction P test, which assuming the data met the normal distribution [23].Publication bias were assessed using both qualitative and quantitative methods, including funnel plot, Egger, and Begg tests [24,25].The P value for pooled conclusions are 2-sided, and P < 0.05 was considered as statistically significant.Statistical analysis in our study was performed by using STATA software (version 12.0; Stata Corporation, College Station, TX, USA).

Search of the literature
An initial electronic searches yields 4,532 records, and 3,246 articles were retained after duplicate records were excluded.Then a total of 3,105 studies were removed owing to these studies reported irrelevant topics.Reviewing the reference lists yields 7 potential included studies, and a total of 148 studies were retrieved for full-text evaluations.After this, 106 studies were excluded because of: other design (n = 54), reported other outcomes (n = 37), no sufficient data (n = 15).Finally, 39 cohorts reported in 42 studies were selected for meta-analysis .

Characteristics of the included studies
The baseline characteristics of included studies and involved individuals are shown in Table 1.A total of 4,389,263 individuals were included, and the sample size in each study ranged from 117 to 975,685.Ten cohorts were performed in Eastern countries (China, Korea, Japan, and Thailand), while the remaining 29 cohorts were conducted in Western countries (USA, UK, Canada, Denmark, Sweden, Finland, Australia, and Poland).Twenty-nine studies designed as prospective cohort, while the remaining 10 studies designed as retrospective cohort.Ten studies used self-report to defined PD, while the remaining 29 studies applied clinical diagnosed for PD definition.The follow-up duration of included studies ranged from 2.9 years to 57.0 years, and the study quality with 6-8 stars.

Major adverse cardiovascular events
The association of PD with the risk of MACEs were available in 17 studies, and the summary RR indicated PD was associated with an increased risk of MACEs (RR: 1.24; 95%CI: 1.15-1.34;P<0.001; Fig 2).The heterogeneity across included studies was substantial (I 2 = 88.9%;P<0.001).Sensitivity analysis was performed to assess the role of single study from the overall analysis, and the results found the pooled conclusion was stability and the heterogeneity was not significantly reduced (S1 File).Subgroup analysis indicated elevated MACEs risk in patients with PD in mostly subgroups, whereas PD was not associated with the risk of MACEs if pooled male individuals, and used self-report as PD definition (Table 2).There was no significant publication bias for the association of PD with the risk of MACEs (P value for Egger: 0.095; P value for Begg: 0.325; S2 File).

Coronary heart disease
A total of 17 studies investigated the association of PD with the risk of CHD.We noted PD was associated with an elevated risk of CHD (RR: 1.20; 95%CI: 1.12-1.29;P<0.001; Fig 3 ), and significant heterogeneity among included studies was observed (I 2 = 89.8%;P<0.001).The pooled conclusion was robustness and not altered by excluding any particular study.Moreover, the heterogeneity was not significantly changed by removing any individual study (S1 File).The significant associations between PD and CHD were observed in mostly subgroups, whereas PD did not affected subsequent risk of CHD if pooled studies conducted in Eastern countries, female individuals, and studies with moderate quality (Table 2).The effect estimates for the relationship between PD and CHD in the subgroups of Western countries (P<0.001), and retrospective cohort studies (P = 0.026) were higher than corresponding subgroups.Although the Begg test indicated no significant publication bias (P = 0.415), while the Egger test suggested potential significant publication bias for CHD (P = 0.029) (S2 File).The conclusions were not changed after adjustment for publication bias by using the trim and fill method [68].

Myocardial infarction
The association of PD with the risk of MI were available in 9 studies, and the summary result indicated PD was associated with an increased risk of MI (RR: 1.14; 95%CI: 1.06-There was significant heterogeneity among included studies (I 2 = 80.1%; P<0.001), and this significant heterogeneity was not significantly altered by removing any particular study.Moreover, the pooled conclusion was stability and not changed by removing any single study (S1 File).Although PD was associated with the risk of MI in mostly subgroups, whereas PD was not associated with the risk of MI if pooled studies conducted in Eastern countries, male individuals, used self-report defined PD, follow-up duration <10.0 years, and studies with high adjusted level (Table 2).No significant publication bias MI were observed (P value for Egger: 0.181; P value for Begg: 0.602; S2 File).

Stroke
A total of 24 studies investigated the association of PD with the risk of stroke.We noted PD was associated with an increased risk of stroke (RR: 1.26; 95%CI: 1.15-1.37;P<0.001; Fig 5), and significant heterogeneity was observed across included studies (I 2 = 94.8%;P<0.001).Sensitivity analysis indicated the pooled conclusion was stability and the heterogeneity was not significantly changed by sequential removing individual study (S1 File).Subgroup analysis found significant association between PD and stroke in mostly subgroups, whereas PD was not associated with the risk of stroke if pooled studies conducted in Eastern countries (Table 2).Region (P = 0.025), PD definition (P = 0.012), and study quality (P = 0.010) could affect the association between PD and stroke risk.There was no significant publication bias for

Cardiac death
The association of PD with the risk of cardiac death were available in 10 studies, and the summary RR indicated PD was associated with an increased risk of cardiac death (RR: 1.42; 95% CI: 1.10-1.84;P = 0.007; Fig 6).There was significant heterogeneity across included studies (I 2 = 91.3%;P<0.001).The pooled conclusion and heterogeneity among included studies were not significantly altered by sequential removing individual study (S1 File).Subgroup analyses found PD was associated with an increased risk of cardiac death when pooled studies conducted in Western countries, studies designed as prospective cohort, male individuals, used clinical diagnosed defined PD, follow-up duration � 10.0 years, and studies with high adjusted level (Table 2).The association of PD and the risk of cardiac death could affected by region (P = 0.012), PD definition (P = 0.014), and follow-up duration (P = 0.010).No significant

All-cause mortality
A total of 12 studies investigated the association of PD with the risk of all-cause mortality.We noted PD was associated with an increased risk of all-cause mortality (RR: 1.31; 95%CI: 1.07-1.61;P = 0.010; Fig 7), and significant heterogeneity was detected among included studies (I 2 = 99.3%;P<0.001).Sensitivity analysis indicated the pooled conclusion was not altered and the heterogeneity was not fully explained by excluding any specific study (S1 File).Subgroup analysis found PD was associated with an elevated risk of all-cause mortality in mostly subgroups, whereas PD did not affected subsequent all-cause mortality risk if pooled studies conducted in Western countries, used self-report defined PD, follow-up duration < 10.0 years, and studies with high quality (Table 2).There was no significant publication bias for all-cause mortality (P value for Egger: 0.914; P value for Begg: 0.150; S2 File).

Discussion
The current systematic review and meta-analysis on the basis of cohort studies and investigated the associations of PD with the risk of MACEs, CHD, MI, stroke, cardiac death, and allcause mortality.This comprehensive, quantitative analysis identified 4,389,263 individuals from 29 prospective cohort studies and 10 retrospective cohort studies across wide range of individuals' characteristics.Our study found PD were associated with elevated risk of MACEs, CHD, MI, stroke, cardiac death, and all-cause mortality.Moreover, the association of PD with the risk of CHD in the subgroups of studies conducted in Western countries, and studies designed as retrospective cohort were greater than corresponding subgroups.Furthermore, PD and subsequent risk of stroke in the subgroups of studies conducted in Western countries, PD with clinical diagnosed, and studies with moderate quality were greater than corresponding subgroups.Finally, the effect estimates for the relation between PD and cardiac death in the subgroups of Western countries, PD with clinical diagnosed, and follow-up duration � 10.0 years were larger than corresponding subgroups.Several systematic review and meta-analyses have already investigated the role of PD with the risk of cardiovascular outcomes and all-cause mortality [13][14][15].Larvin et al identified 30 cohort studies and found the MACEs risk was significantly elevated in PD patients, and the risk increased highest was stroke [13].Qin et al performed a meta-analysis of 10 cohort studies and found PD was associated with an increased risk of MI, while this association could affected by sex, effect value, survey form, and study quality [14].Leng et al identified 26 studies and found significant association between PD and MACEs in both men and women [15].However, several other important outcomes, including cardiac death, and all-cause mortality were not investigated.Moreover, whether the associations of PD with the risk of cardiovascular outcomes and all-cause mortality could affected by individuals' characteristics were not fully illustrated.Therefore, the current study was performed to assess the role of PD with subsequent cardiovascular outcomes and all-cause mortality risk.
This study found PD were associated with elevated risk of MACEs, CHD, MI, stroke, cardiac death, and all-cause mortality.The potential mechanism for these relationships included: (1) The PD pathogens entering the blood can directly invade the cardiovascular endothelial cells and smooth muscle cells, which significantly associated with the risk of vascular diseases.Moreover, the pathogens could colonize at atherosclerotic plaque, pericarditis or myocardial tissue after enter blood, which could affect the occurrence and development of coronary heart disease, occurrence and development of coronary heart disease [69][70][71]; (2) Porphyromonas gingivalis, as one of the main pathogens of PD, it can induce the expression of platelet aggregation and intercellular adhesion molecule-1, vascular cell adhesion molecule-1 and P-selectin.In addition, the arginine-specific cysteine proteinase R released by it can induce CVD by activating protein C, coagulation factor X and prothrombin [72]; (3) PD pathogens could induce systemic inflammation, which demonstrated inflammation was considered as a predisposing factor for CVD [73,74].PD patients were associated with elevated levels of C-reactive protein and other inflammatory markers in the circulation, which could promote the progression of systemic inflammation and CVD [75,76]; (4) Oral pathogens could cross the gingival epithelial-conjunctival barrier and vascular endothelial cells, then reached the blood, causing the inflammation and immune response in blood vessels [77][78][79][80]; (5) PD pathogens could induce myocardial hypertrophy via activated oxidative stress pathway [81]; and (6) PD was associated with a reduced vascular endothelial function in the gingival tissue, and damage of vascular function, then caused excess risk of stroke [82].
Subgroup analyses found the associations of PD with the risk of CHD, stroke, and cardiac death could affected by region, study design, PD definition, follow-up duration, and study quality.Several reasons could explained these results: (1) the excess risk of CHD, stroke, and cardiac death related to PD in Western countries might caused by older age and severity of PD.Moreover, large number of included studies were performed in Western countries, and the conclusions was robust with narrow 95%CI; (2) although effect estimate for the relation between PD and CHD in retrospective cohort studies was large than prospective cohort studies, while these results was variable owing to only 3 included studies designed as retrospective cohort.Moreover, prospective cohort studies could eliminate selection and recall bias that might be concerned of retrospective cohort studies; (3) the definition of PD applied clinical diagnosis was more accuracy than self-report, and the severity of PD could affect the effect estimates of cardiovascular outcomes [13]; (4) considering the progression of cardiac death related to PD are slowing, longer follow-up duration could observed large number of cardiac death, thus the power was enough to detect potential association; and (5) the methodological quality were assessed based on selection, comparability, and outcome, which is significantly related to the reliable of pooled conclusion.Moreover, smaller number of studies with moderate quality, and the results not stability.
Several strengths of this study should be mentioned.First, the analysis on the basis of cohort studies, and the conclusion could proved causality relationship.Second, the analysis based on large sample size, and the conclusions of this study was robust than any single study.Third, the exploratory analyses were performed according to region, study design, gender, PD definition, follow-up duration, adjusted level, and study quality, and the differences between subgroups were compared.Finally, the pooled conclusions in our study was robust and not changed by removing any particular study.
The limitations of this study included: (1) the analysis contained both prospective and retrospective cohort studies, and the selection and recall biases were inevitable; (2) the severity of PD were not addressed, which could affect the strength for the associations of PD with the risk of cardiovascular outcomes and all-cause mortality; (3) there were significant heterogeneity across included studies for cardiovascular outcomes and all-cause mortality, which not fully explained by sensitivity and subgroup analyses; (4) the adjusted factors across included studies are differing, which play an important role on the risk of cardiovascular outcomes and allcause mortality; and (5) inherent limitations for meta-analysis of published data, including inevitable publication bias and restricted detailed analyses.

Conclusions
This study found PD were associated with an increased risk of MACEs, CHD, MI, stroke, cardiac death, and all-cause mortality.Moreover, region, study design, PD definition, follow-up duration, and study quality might affect the strengths for the associations of PD with the risk of CHD, stroke, and cardiac death.Thus, individuals with PD should be early identified to prevent the progression of cardiovascular outcomes and all-cause mortality.Further large-scale prospective studies should be performed to assess whether the treatments for PD could reduce the risk of cardiovascular outcomes and all-cause mortality.
Fig 1 presented the details of literature search and study selection.